Comparison of nitrogen balances and efficiencies in rice cum prawn vs. rice cum fish cultures in Mymensingh, North-Eastern Bangladesh

This on-site study is a comparison between integrated rice cum prawn and rice cum fish cultures and their efficiencies in North-Eastern Bangladesh. Common rice cultivation practices in this area often cause environmental problems due to inadequate use of chemical fertilizers and addition of animal feed with fishmeal. Problems include eutrophication and the reduction of soil fertility, as well as the reduction of organic matter content, water holding capacity and the inefficient use of N due to leaching, run-off and denitrification. We evaluated major N inputs of additional feed and chemical N fertilizer into the rice paddy over three field seasons. The N content of rice grain did not increase significantly with fertilizer supply ranging from 41.18 ± 5.57 kg/ha to 57.07 ± 3.62 kg/ha. However, the supply of fertilizer significantly increased the N content of rice straw, consisting of stem, leaf and leaf, ranging from 27.69 ± 6.80 kg/ha to 64.78 ± 2.21 kg/ha. In addition, the supply of feed let to a significant increase of crude lipid per hectare of all integrated animal species, but not of crude protein. These results question the efficiency and economic viability of using chemical fertilizers and feed in integrated cultures. Compared to rice cum fish cultures, unfed and unfertilized rice cum prawn cultures achieved economically satisfying results in terms of the N-output of the major compounds and the N balance (ΔN). Our findings suggest that rice cum prawn cultures without chemical fertilization and without additional feed are economically possible and thus highly recommendable for small scale farmers as they reduce negative environmental impacts. This study can therefore guide future agricultural and aquacultural management practices to help improve fertilization techniques and feed supply.